1. Field of the Invention
This invention relates generally to fluid dynamic bearings and more specifically to a fluid dynamic bearing motor assembly configured with an integrated counterplate to contain bearing fluid within the assembly.
2. Description of the Background Art
FIG. 1 is an exploded perspective view illustrating a prior art disc drive 100. As shown, disc drive 100 may include, without limitation, a housing 105, a shaft 130, discs 135 and a suspension arm assembly 150. Housing 105 includes a base 110 that is attached to a cover 115. In addition, a seal 120 may be disposed in between base 110 and cover 115. One or more discs 135, which have surfaces 140 covered with a media configured to store information, are attached to shaft 130. During operation, suspension arm assembly 150 is configured to suspend read/write heads 145 above surfaces 140 as a spindle motor (not shown) rotates discs 135 about shaft 130 at high speed. Suspension arm assembly 150 is further configured to move read/write heads 145 radially across surfaces 140 to position read/write heads 145 above different radially spaced tracks (not shown) disposed on surfaces 140 where encoded information may be stored within the media. Once positioned, read/write heads 145 may either read encoded information from or write encoded information to the media at selected locations.
FIG. 2 is a cross-sectional view illustrating a fluid dynamic bearing motor assembly 200. Fluid dynamic bearing motors, such as fluid dynamic bearing motor assembly (hereinafter “FDB motor assembly”) 200, oftentimes are used in precision-oriented electronic devices to achieve better performance. For example, using a fluid dynamic bearing motor in a disc drive, such as disc drive 100 described above in conjunction with FIG. 1, results in more precise alignment between the tracks of the discs and the read/write heads. More precise alignment, in turn, allows discs to be designed with greater track densities, thereby decreasing the size of the discs and/or increasing the storage capacity of the discs.
As shown, FDB motor assembly 200 includes, without limitation, a shaft 202, a sleeve 206, a counterplate 208, a thrust plate 210, fluid dynamic thrust bearings 212 and 214, a capillary seal 216 and a protective shield 222. Shaft 202 is attached to a top cover 209 of a disc drive housing and is configured to remain stationary. Thrust plate 210 is attached to shaft 202 and therefore also remains stationary. Thrust plate 210 is configured to provide thrust surfaces for fluid dynamic thrust bearings 212 and 214 and a seal wall 220 for capillary seal 216. Sleeve 206 is configured to rotate about a rotational axis 204 and to provide a thrust surface for fluid dynamic thrust bearing 214. Counterplate 208 is attached to sleeve 206 and therefore rotates about rotational axis 204 as well. Counterplate 208 is configured to provide a thrust surface for fluid dynamic thrust bearing 212 and a seal wall 218 for capillary seal 216. Bearing fluid fills gaps 213 and 215 between surfaces of thrust plate 210 and facing surfaces of counter plate 208 and sleeve 206. As is well known to persons skilled in the art, appropriate pumping grooves (not shown) are provided along one or more thrust surfaces of each of fluid dynamic thrust bearings 212 and 214 to create localized regions of high pressure to support the axial load generated by the rotating elements of FDB motor assembly 200.
Attaching shaft 202 to top cover 209 provides shaft 202 with additional stiffness, which decreases vibration and non-repetitive run-out, thereby improving the performance of FDB motor assembly 200. As persons skilled in the art will recognize, one consequence of such a configuration is that an additional opening 221 into the bearing fluid is created. To prevent bearing fluid from escaping from FDB motor assembly 200 during normal operation and when FDB motor assembly 200 is subjected to shocks, various elements, may be added to FDB motor assembly 200. One such approach, set forth in the embodiment of FIG. 2, includes adding elements such as capillary seal 216 and protective shield 222 to FDB motor assembly 200.
Capillary seal 216 acts to maintain the bearing fluid within a bearing fluid reservoir 217. Protective shield 222 is coupled to counter plate 208 and has a distal end 226 disposed in close proximity to shaft 202. Among other things, protective shield 222 acts as a splash guard to prevent bearing fluid that splashes out of fluid reservoir 217 upon a shock from escaping from FDB motor assembly 200.
In addition, an exclusion seal (not shown) may be added at a location 224 to prevent bearing fluid that splashes out of bearing fluid reservoir 217 upon a shock from escaping from FDB motor assembly 200 through the gap between distal end 226 of protective shield 222 and shaft 202. Typically, an exclusion seal is an additional element added between distal end 226 and shaft 202. In some instances, however, protective shield 222 may be configured to provide an exclusion seal by bending distal end 226 such that a capillary seal may be formed between protective shield 222 and shaft 202.
As the foregoing illustrates, an approach to containing the bearing fluid within FDB motor assembly 200 that includes adding fewer elements to FDB motor assembly 200 is desirable because adding fewer elements simplifies the design and assembly of FDB motor assembly 200.